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Hardness of cooked soybeans [Glycine max (L). Merr.] is an important attribute in food processing. We found one candidate gene, Glyma03g03360, to be associated with the hardness of cotyledons of cooked soybeans, based on a quantitative trait locus and fine-scale mapping analyses using a recombinant inbred line population developed from a cross between two Japanese cultivars, "Natto-shoryu" and "Hyoukei-kuro 3". Analysis of the DNA sequence of Glyma03g03360, a pectin methylesterase gene homologue, revealed three patterns of mutations, two of which result in truncated proteins and one of which results in an amino acid substitution. The truncated proteins are presumed to lack the enzymatic activity of Glyma03g03360. We classified 24 cultivars into four groups based on the sequence of Glyma03g03360. The texture analysis using the 22 cultivars grown in different locations indicated that protein truncation of Glyma03g03360 resulted in softer cotyledons of cooked soybeans, which was further confirmed by texture analysis performed using F2 populations of a cross between "Enrei" and "LD00-3309", and between "Satonohohoemi" and "Sakukei 98". A positive correlation between hardness and calcium content implies the possible effect of calcium binding to pectins on the hardness of cooked soybean cotyledons.

Hydroperoxide and n-hexanal production by lipoxygenase action is an important problem in the effective use of soybean seeds for food ingredients. We examined here the additional effect of unsaturated fatty acids on the 1,3-diethyl-2-thiobarbituric acid (DETBA) value (index for hydroperoxide production) and n-hexanal production with two normal soybean cultivars; three mutants partially lacking lipoxygenase and containing only L-1, L-2, or L-3; and one mutant completely lacking lipoxygenase (L0). Among the soybeans tested, the L0 soybean had the lowest levels of both DETBA value and n-hexanal production. The low DETBA values were maintained over a wide range of pH (4−10) and temperature (4−70 °C) and were not influenced by the addition of unsaturated fatty acids. These results suggest that the L0 soybean could be an excellent soybean source for making soybean products with a combination of soybean and other food ingredients. Keywords: Soybean; lipoxygenase isozymes; hexanal; DETBA value; lipid peroxidation;...

Soybean lipoxygenases are responsible for the generation of undesirable flavors which limit wide utilization of soybeans in food products. Lipoxygenase-lacking mutants are expected to be soybeans with improved flavors. In this study, the accumulation of hexanal and the 1,3-diethyl-2-thiobarbituric acid (DETBA) value in homogenates were determined from two normal soybean cultivars (L 123(S) and L 123(F) , three soybean cultivars with L-1 (L 1 ), L-2 (L 2 ), and L-3 (L 3 ), and one soybean cultivar lacking all three lipoxygenase isozymes (L 0 ). Hexanal accumulation in the homogenates was in the order L 2 >L 123(S) >L 123(F) >L 1 >L 3 >L 0 . The DETBA value in the homogenates was in order L 123(S) , L 123(F) >L 2 , L 3 >L 1 , L 0 . Such cultivar differences were induced after the soaked soybeans were ground or after the soybean flour was wetted. These results suggested that L 0 could become a superior soybean for food ingredients, concerning flavors originating from lipoxygenases

A simple and rapid spectrophotometric and visual judging method was developed for the selective detection of individual lipoxygenase isozymes (L-1, L-2, and L-3) in soybean [Glycine max (L.) Merrill] seeds, based on the bleaching activities of these isozymes in contact with methylene blue and β-carotene. The method consists of three procedures designated tests I-III. The tests are performed by mixing soybean extract samples or wetted soybean flour with each dye-substrate of test I for the L-1 isozyme, test II for the L-2 isozyme, and test III for the L-3 isozyme, whereupon the presence of individual isozymes contained in the soybean is determined spectrophotometically or visually within 10 or 5 min, respectively. In the visual judging method available as a routine screening test, the total amount of soybean flour required for the three tests is only about 10 mg